You can achieve this by creating a at Cost Price Sheet!
You will need to go into your Store and Create a New Price Sheet
Make sure that you have not accidentally selected this price sheet as your default price sheet. If you have this means that all new Collections will have this price sheet attached and your clients will be able to purchase the items without your markup.
Once you have named the Price Sheet and Selected the Lab of choice click Save.
After you have added products to the Price Sheet you will need to remove all Markup that has been added to the products.
You can do this by selecting "Bulk Markup" and setting the Markup Percentage to zero (or leave it blank) and also set "No Rounding". This will make sure that you are only charged the cost of the Lab, once you have the correct settings select "Apply to All"
If you have correctly set your Price Sheet to not have any Markup it should look like this:
Now that you have finished creating your At Cost Price Sheet, you must go and attach it to the Collection you wish to purchase prints at Cost For.
You can do this by going into the Collection > Collection Settings > Store > Price Sheet and select the Lab Cost Price Sheet.
Note: Be sure to remember to change the Price Sheet back after you have ordered the prints at cost because anyone with access to the collection will also be able to purchase prints at cost while this is the active Price Sheet. You can follow the same steps to change it back to your original Price Sheet.
Here is what it will look like when you go to purchase prints:
Once you have set the Lab Cost Price Sheet with the Collection, you will need to enter the Collection like a Client would and order your images through the same process. Here is what the Pricing will look like when an image to purchase.
Once you have selected all your desired images, click checkout and begin the checkout process! You've now successfully ordered prints at cost. Don't forget to go back into the Collection and attach the Correct Price Sheet!